The following references to, and descriptions of, prior proposals or products are not intended to be, and are not to be construed as, statements or admissions of common general knowledge in the art. In particular, the following prior art discussion does not relate to what is commonly or well known by the person skilled in the art, but assists in the understanding of the inventive step of the present invention of which the identification of pertinent prior art proposals is but one part.
A type of wheel capable of multiple directional travel (while the main axis of rotation remains oriented in the same direction) has been described variously as an omniwheel and multi-directional wheel. Such wheels include a central hub rotatable about a main axis and a plurality of independently mounted rotatable rollers located about the rim of the hub. The rollers are each capable of rotation about an axis normal to and radially spaced from the main axis, whereby the wheel is capable of moving in a first direction in which the wheel rotates about the main axis or in a transverse direction in which one or more rollers contacting the ground rotate about their corresponding axes.
One such wheel has been described in International Patent Application No. PCT/AU01/01175 (publication No. WO02/24471). The multiple directional wheel described therein comprised a circular wheel frame having a plurality of circumferentially spaced peripheral axles on which were mounted a pair of parallel rings of rollers offset relative to one another. The frame included an integrally formed polyaxled ring that required the rollers to be molded over the axles and limited the range of molding techniques that could be utilized. The rollers rotated about multiple axes normal to a main axis of the wheel. The roller axes were each aligned substantially normal to lines extending radially from the main axis through the midpoint of each roller axis. The rollers were positioned to provide a large overlap (20%-35% in side view) of effective ground contacting surface between diagonally adjacent rollers.
Further improvement to such types of wheels has been described in International Patent Application No. PCT/AU2003/001002 (publication No. WO2004/014667), the entire contents of which is herein incorporated by reference. That disclosure described a method of construction of a frame on which was mounted a single row of rollers. The single row frames were able to be joined to like frames, in offset orientation, to form multiple rowed wheels having good ground contacting overlap between diagonally adjacent rollers. The method of forming the wheel involved each roller being mounted onto a wrap-around bush, which, in turn, was mounted to one of the multiple axles.
An object of the present invention is to ameliorate the aforementioned disadvantages of the prior art or to at least provide a useful alternative thereto.